Silicone polyethers (SPEs) are used extensively in a variety of surfactant applications, such as in the production of polyurethane foams, and as ingredients in personal care products. SPE's are typically based on copolymer structures of polyorganosiloxanes having pendant polyoxyalkylene groups. Most commonly, the copolymer structures of silicone polyethers are the “rake” type, where a predominately linear polyorganosiloxane provides the “backbone” of the copolymer architecture with pendant polyoxyalkylene groups forming the “rake”. “ABA” structures are also common, where a pendant polyoxyalkylene group is at each molecular terminal of a linear polyorganosiloxane. (AB)n silicone polyether block copolymers are also known.
Commercially, silicone polyethers are typically made via a platinum catalyzed hydrosilylation reaction in large batch reactors. Because of the significant volumes of silicone polyethers used commercially, a continuous process for their preparation would be desirable. However, attempts to produce silicone polyethers via continuous processes have been limited due to the complexities of the hydrosilylation reaction mechanism. In particular, the production of silicone polyethers via a continuous process often will result in a greater formation of hydrolyzable —Si—O—C— bonds vs. comparable batch reactions, especially if the process is conducted solventless. Typically a large molar excess of the unsaturated polyether is needed in such hydrosilylation reactions. Since it is impossible to separate the silicone polyether product from un-reacted unsaturated polyether starting materials, product quality and performance is limited in certain applications. Thus, there is a need to identify processes to prepare silicone polyethers that are suitable for continuous processing techniques.
The present inventors have discovered a method for preparing silicone polyethers of improved quality. In particular, the inventive process produces silicone polyethers having less hydrolyzable Si—O—C bonds. The present invention is particularly useful to prepare silicone polyethers via a continuous hydrosilylation process.